1. Field of the Invention
The present invention relates to vehicle safety accessories, and particularly to a tilt angle sensor layout structure for a vehicle, and a vehicle incorporating such a tilt angle sensor.
2. Description of the Background Art
It is well known that off-road recreational vehicles such as, for example, all-terrain vehicles (ATVs) may drive over all different types of terrain, and often will be driven up steep hills or on terrain that is angled at a grade. It has been known to use tilt angle sensors in ATVs as a safety feature. A tilt angle sensor is used to detect, for example, a tilt angle in the left-right direction of a vehicle. When the vehicle is inclined to such an extent that the tilt angle exceeds a predetermined angle, the engine is forcibly stopped. This can be achieved, for example, by stopping the ignition power supply to the engine, or alternatively, by stopping the fuel supply to the engine.
It is known to provide a layout structure for such a tilt angle sensor in a vehicle in which a rollover sensor is also provided, in the vicinity of a steering shaft and on the front side of a fuel tank. Such a layout structure is disclosed in Japanese Patent Laid-open No. 2005-178420.
FIGS. 8 and 9 are reproductions of FIGS. 1 and 7, respectively, of Japanese Patent Laid-open No. 2005-178420, in which the reference numbers have been modified from those in the original document. In FIG. 8, it is shown that a front portion of a fuel tank 203 is provided with a recessed portion that permits the steering shaft 209 to pass therethrough, and rollover sensors 246 and 247 are disposed in the recessed portion. In addition, as shown in FIG. 9, Japanese Patent Laid-open No. 2005-178420 discloses that a bar 222 is bridgingly provided between left and right main frames 220, 220, two sub frames 223, 223 are extended from the bar 222 toward the vehicle rear side, a stay 224a, 224b is bridgingly provided between the sub frames 223, 223, and the rollover sensors 246 and 247 are attached to the stay 224a, 224b. 
When the two rollover sensors 246 and 247 are disposed in the recessed portion provided at the front portion of the fuel tank 203, it is necessary, for avoiding interference with the rollover sensors 246 and 247, to form the recessed portion in a large size, or to space the recessed portion away from the rollover sensors 246 and 247. These requirements influence the shape and layout of the fuel tank 203.
On the other hand, a center of turning of the vehicle is present in the vicinity of the steering shaft 209. Therefore, where the rollover sensors 246 and 247 are disposed at such a center of turning, it is possible to reduce the possibility of the sensors being influenced by centrifugal force at the time of turning of the vehicle; accordingly, it is desired to lay out the rollover sensors 246 and 247 in the vicinity of the center of turning of the vehicle, without influencing the shapes and layout of such component parts as the fuel tank 203.
Furthermore, it is desirable to adopt a layout structure in which the stay 224a, 224b that supports the rollover sensors 246 and 247 is attached to a higher-rigidity portion of a vehicle body frame, so as to minimize an influence of vibrations of the vehicle body, and in which the rollover sensors 246 and 247 can be protected against flying stones and the like coming from the vehicle body front side.
It is an object of the present invention to provide a tilt angle sensor layout structure such that the tilt angle sensor is less liable to be influenced by a centrifugal force at the time of turning of the vehicle or by vibrations of the vehicle body.
It is another object of the present invention to provide a tilt angle sensor layout structure configured such that it is unnecessary to change the shapes and layout of other component parts provided on the vehicle body.
It is still another object of the present invention to provide a tilt angle sensor layout structure in which the tilt angle sensor can be protected against flying stones and the like coming from the front end of the vehicle body.